and mostly closes. The “stops” actually prevent the capacitor from going completely
from open to closed.
Putting a knob on the tuning shaft makes turning it MUCH easier! If the shaft cannot be
turned the full 5 revolutions, then use a small screwdriver to separate the ones that are
sticking. Spray a little more WD-40 on the “stops”. You may have to force the shaft in
the direction which the full 5 revolutions would normally be made. Work the shaft “back
and forth” until the “stops” break free. Then, run the shaft back and forth several times
the full 5 revolutions. If the shaft is still hard to turn, put a little WD-40 on the “worm
gear” at the rear of the shaft which activates the gear which rotates the variable
capacitor.
Then, put a lubricant of your choice on the pivot points on the air variable capacitor.
Although cleaning the old lubricant from the pivot points often eliminates the “warble”, it
will often return in a relatively short period of time. To prevent the “warble” from
returning, a short piece of braid has to be connected between the shaft of the rotor on
the variable capacitor and the frame of the capacitor. Various persons have devised
ways to connect this braid. The method described herein is pretty simple to do and is
very effective.
Before continuing, it is necessary to note that there are at least 2, maybe more, systems
of getting from the worm gear of the main tuning shaft and the variable capacitor. Both
use a gear on the shaft of the variable capacitors but those gears are very different. The
earlier version, Heath part number 110-32, uses a large diameter gear that is relatively
thick and the later version, Heath part number 110-40, uses a relatively small diameter
gear that is fairly thin. The method of attaching the braid to the shaft is similar, but
different approaches have to be made.
There are 2 setscrews which hold the gear onto the variable capacitor shaft. One of
those setscrews is exposed when the variable capacitor is almost fully open (minimum
capacitance) and the other is exposed when the capacitor is about halfway open. It is
the setscrew that is exposed when the capacitor is halfway that is of interest. Remove
this setscrew. Sometimes this setscrew has a normal “slot” and sometimes it requires
an Allen wrench (NOT a Bristol).
Acquire a piece of braid about 2-inches long. This can be tinned or not. Using braid from
a short piece of RG58/U coaxial cable works great.
Now comes the difference between the LMO with the large gear and one with the
smaller gear. With the large gear, cut off a length of 8-32 machine screw about 1/2th
inch long, so that you just have the thread portion. That is, no “head” on the screw.
Heathkit Linear Master Oscillators (LMOs) Page 125
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